Ice making machines, or ice makers, typically comprise a refrigeration and ice making system that employs a source of refrigerant flowing serially through a compressor, a condenser, a thermal expansion valve, and an evaporator assembly. Thermally coupled to the evaporator assembly is a freeze plate comprising a lattice-type cube mold. Additionally, typical ice makers employ gravity water flow and ice harvest systems that are well known and in extensive use. Ice makers having such a refrigeration and ice making system are often disposed on top of ice storage bins, where ice that has been harvested is stored until it is needed. Such ice makers have received wide acceptance and are particularly desirable for commercial installations such as restaurants, bars, motels and various beverage retailers having a high and continuous demand for fresh ice.
In these ice makers, water is supplied at the top of a freeze plate which directs the water in a tortuous path toward a water pump. A portion of the supplied water collects on the freeze plate, freezes into ice and is identified as sufficiently frozen by suitable means whereupon the freeze plate is defrosted such that the ice is slightly melted and discharged therefrom into an ice storage bin. Typically, these ice machines can be classified according to the type of ice they make. One such type is a grid style ice maker which makes generally square ice cubes that form within individual grids of the freeze plate which then form into a continuous sheet of ice cubes as the thickness of the ice increases beyond that of the freeze plate. After harvesting, the sheet of ice cubes will break into individual cubes as they fall into the ice storage bin. Another type of ice maker is an individual ice cube maker which makes generally square ice cubes that form within individual grids of the freeze plate which do not form into a continuous sheet of ice cubes. Therefore, upon harvest individual ice cubes fall from the freeze plate and into the ice storage bin. Control means are provided to control the operation of the ice maker to ensure a constant supply of ice. Various embodiments of the present invention can be adapted to either type of ice maker, and to others not identified, without departing from the scope of the present invention.
Traditionally, the principal components of a refrigeration and ice making system for use in an ice maker include a source of refrigerant flowing serially through a compressor, a condenser, a thermal expansion valve, and an evaporator assembly. The evaporator is thermally coupled to the freeze plate in order to freeze the supplied water into ice.
The cooling cycle of the ice maker is comprised of two sub-cycles, the sensible cooling cycle and the latent cooling cycle. During the sensible cooling cycle the supplied water is and continuously recirculated by a water pump across the freeze plate and back to the sump thereby cooling the supplied water. Once the supplied water reaches the freezing point the supplied water begins to freeze in the freeze plate, the latent cooling cycle begins.
However, in certain situations, the water in the sump can fall below the freezing point of water before ice begins to freeze in the freeze plate. As a result, it is not uncommon for the water in the sump to begin “slush up.” A “slush-up” situation happens when the water that is being recirculated over the freeze plate sub-cools below 0° C. (32° F.) and then suddenly begins to freeze. Ice crystals in the sub-cooled water can quickly propagate through all of the water in the sump, turning all of the sub-cooled water to slush. When this happens, the water cannot be pumped from the sump across the freeze plate, thus terminating any water flow in the ice maker. Accordingly, the ice machine will stop refrigerating the water and ice production will cease. This “slush up”condition can last for several minutes until the water in the sump warms and the slush thaws back into liquid water. This “slush up” condition represents inefficiency in the cooling cycle because the water is not being cooled for a period of time. Additionally, the time required to produce ice is extended until the slush dissipates enough for the water to resume flowing through the ice making system.
Prior art ice machines have attempted to solve this problem by turning off the water pump for a short period of time during each ice production cycle. By not flowing water over the freeze plate for a short period of time, the temperature of the evaporator can be reduced such that when the water pump is turned back on and water again flows over the freeze plate, the water will freeze on the freeze plate more quickly and the water will not sub-cool. This approach requires a properly calibrated temperature sensor to work, and turning off the water pump lengthens the freeze cycle and thus is not the most efficient way to make ice. However, this method does prevent the “slush up” problem.
Therefore, there is a need in the art to prevent a “slush up” in the sump of an ice maker without turning off the water pump thus avoiding the resulting delay in the ice making process. Likewise, there is a need in the art to prevent a “slush up” in the sump of an ice maker without the use of an additional thermostat which adds complexity and cost to the system and has the potential to fail or be mis-calibrated.